The prior art uses displacement pistons in tool turrets, which displacement pistons are movable by pressure activation and which can be actuated by a pressure fluid control device, in order to realize switching operations. These operations may involve the locking of the rotational movement of the turret head relative to the housing or the activation of a slide coupling between a motorized drive device and a machining tool to be driven. Document DE 41 16 774 C1 for example presents a tool turret in which, in order to lock the rotational movement of the turret head relative to the housing, coaxial Hirth teeth are provided on the housing and on the turret head, with which, for the purpose of locking, teeth on a displacement piston engage. The displacement piston is pressure activated. Document DE 10 2009 042 772 A1 discloses a drive device in a tool turret in which, to switch a slide coupling, the drive shaft of the coupling forms a displacement piston, which is hydraulically movable for the switching operations of the coupling.
For the operating control of the corresponding tool turret, control of the switching operations realized by the sliding piston is essential. This control usually involves an inductive proximity switch detecting the piston position in an end position. Because suitable proximity switches require a lot of installation space and because they are also costly, detection of only one end position of the piston has been possible until now.